Impact resistant face shield for sporting helmets

ABSTRACT

An impact resistant face shield that includes a single formed arcuate lens portion that, in a first orientation, has a first curvature extending in a horizontal direction and a second curvature extending in a vertical direction. The lens portion has a top portion and a bottom portion that extends relatively inwardly towards the face of the wearer relative to an intermediate portion disposed between the top and bottom portions. Each curvature of the lens defines an arc of a circle having a substantially uniform radius to produce nominal levels of distortion, thereby reducing the prism effects created by the lens, and providing an optically corrected viewing window.

BACKGROUND OF THE INVENTION

This invention relates to mechanical protective devices, and moreparticularly to impact resistant face shields for use in protecting theface of an individual.

Today, sports are more popular than ever. This increase in popularityhas resulted in an increase in the number of amateur and professionalsport participants. Unfortunately, increased participation has resultedin an increase in the number of injuries suffered by individuals, andparticularly in the number of facial injuries. Consequently, some sportsnow recommend and/or require the use of face shields or other facialprotective devices when participating in the sport. One such sport ishockey.

Conventional face shields suitable for use in sports, such as thosemanufactured by Itech Sports Products, Inc. under the trade designationITECH® Type IV sports protector, typically consist of a transparentpolycarbonate blank that is formed or molded into a convex shield, whichis adapted for mounting to existing sport helmets. The shield, whenmounted to the helmet, extends generally outwardly and away from thewearer's face. As a result of this mounting configuration, objectslocated in the external environment appear at least partially distorted.Thus, the molded polycarbonate blank introduces some distortion over aportion of the individual's field of view.

The distorting effects of conventional face shields creates a unique setof problems for the wearer. The shield can cause strain on the wearer'seyes, which over a period of time can have deleterious effects.Additionally, rapidly viewing objects through the face shield andconversely not through the face shield produces further eye strain byrequiring the individual to focus differently for each different fieldof view.

Due to the foregoing and other shortcomings of existing face shields, anobject of this invention is to provide a face shield that reducesoptical distortion.

Another object of this invention is to provide a protective face shieldthat has relatively high optical clarity and resolution.

Still another object of the invention is to provide a face shield thatreduces the eye strain.

Yet another object of the invention is to provide a face shield that isrelatively strong and durable and relatively lightweight.

Other general and more specific objects of the invention will in part beobvious and will in part appear from the drawings and description whichfollow.

SUMMARY OF THE INVENTION

The present invention relates to protective face shields that providefor higher image resolution and contrast during use. The improvedcontrast and resolution is achieved by providing an impact resistantface shield that addresses optical and mechanical concerns.Specifically, the present invention provides for an optically-correctface shield.

The invention attains an optically correct face shield by structuringthe face shield to have an inner radius, an outer radius, a thicknessand a refractive index, where the foregoing are mated to provide for ashield that lies between a truly plano lens and a lens having concentricgeometry, e.g., constant thickness. The optical qualities of the lensare such that the prism and dioptric power are relatively low, andpreferably between about 0.01 diopter and about 0.10 diopter.

The face shield preferably includes a single formed arcuate lens portionthat, in a first orientation, has a first curvature extending in ahorizontal direction and a second curvature extending in a verticaldirection. The lens portion has a top portion and a bottom portion thatextends relatively inwardly towards the face of the wearer relative toan intermediate portion disposed between the top and bottom portions.Each curvature of the lens defines an arc of a circle having asubstantially uniform radius to produce nominal levels of distortion,thereby reducing the prism effects, e.g., non-uniform distortions of thefield, created by the lens, and providing an optically corrected viewingwindow.

According to one aspect, the lens portion of the face shield of thepresent invention has a thickness defined between outer and innersurfaces. The surfaces preferably have different radii of curvaturesabout centers that are shifted relative to each other. This eccentricityshifts one surface with respect to the other, to create a curved lensthat has a thickness d that varies along the arc length of the faceshield. The diametral lines of the surfaces are shifted such that theinner surface is moved back from a concentric position, thickening thecentral portion of the lens, and creating edges that are thinnerrelative to the central thickened region. This variable thickness, andparticularly the thinning effect of the lens at the edges, opticallycorrects the lens at the peripheral regions by reducing the occurrenceof prismatic deviations and overall prism imbalance.

According to another aspect of the invention, the shield preferablyincludes a frame structure that is formed about at least a portion ofthe lens. According to one embodiment, the frame includes ventilationapertures formed in a top portion of the face shield. The ventilationapertures allow air to flow through the mask to provide for properventilation of the shield to resist or remove fogging.

According to another practice of the invention, the face shieldsurrounds a substantial portion of the wearer's face when situatedproperly thereabout. In this position, the inside surface of the lens issubstantially non-oblique relative to the wearer's face and the wearer'sfield of view is substantially normal to the inside surface of the lensabout most of the field of view. Additionally, the face shield extendsin the vertical direction a distance sufficient to include a substantialportion of the downward field of view without imposing upon the wearerthe distortions and aberrations created by the edges of the shield.

The present invention further pertains to a face protective shieldhaving a shield body formed of strong clear polymeric material having aperipheral region and a central region. The peripheral region includesan attachment clement for securing the shield body in front of thewearer's face. The central region is preferably formed as a viewingwindow sized to extend around in front of the wearer's face. Accordingto one aspect, the shield has a thickness effective to survive impactwithout cracking and curves in both horizontal and vertical planes oversubstantially the entire central region to introduce a degree of lensingand correct viewing aberrations.

According to another aspect, the central region has front and rearsurfaces. The front surface has a radius of curvature R_(f) greater thanthe rear surface radius of curvature R_(r), such that R_(f) -R_(r) =δ.According to still another aspect, the centers of curvature of the frontand rear surfaces are spaced closer than δ.

According to another aspect, the lensing power of the shield is negativein at least the horizontal plane.

Other general and more specific objects of the invention will in part beobvious and will in part be evident from the drawings and descriptionwhich follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following description and apparentfrom the accompanying drawings, in which like reference characters referto the same parts throughout the different views. The drawingsillustrate principles of the invention and, although not to scale, showrelative dimensions.

FIG. 1 is a side view of a first embodiment of the face shield of thepresent invention.

FIG. 2 is a front view of the face shield of FIG. 1.

FIG. 3 is a schematic representation of light rays impinging upon aconventional plano lens.

FIG. 4 is a cross-sectional view of the face shield of FIG. 2 takenalong lines 4--4 illustrating the varying thickness of the shield of thepresent invention.

FIG. 5 is a front view of a second embodiment of the face shield of thepresent invention.

FIG. 6 is a side view of the face shield of FIG. 5.

FIG. 7 is a front view of a third embodiment of the face shield of thepresent invention.

FIG. 8 is a perspective view of the face shield of FIG. 5 mounted to aconventional sporting helmet.

FIG. 9 is a perspective view of the face shield of FIG. 7 mounted to aconventional sporting helmet.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS

FIGS. 1-4 illustrate the general principles of the protective faceshield of the present invention. These general principles pertain toeach of the additional face shield embodiments set forth and describedbelow.

FIGS. 1 and 2 illustrate a first embodiment of the face shield 10 of thepresent invention. The face shield 10 includes a unitary curved lensportion 12 that is encompassed by a beaded frame structure 14 disposedabout a substantial portion of the periphery of the lens. Preferably,the beaded frame 14 is integrally molded with the lens portion 12.

The lens portion 12 has a first or horizontal curvature 16 (as seen in ahorizontal plane), and a second vertical curvature 18. The horizontalcurvature 16 has a circular cross-section and approximates a completesemi-circle, e.g., subtends an arc of about 180°, and thus provides awrap-around face shield that covers and protects the face of the wearerwhile providing a window portion that extends about a substantialportion of the wearer's potential field of view. The potential field ofview is substantially greater than the actual view of any moment, andincludes the extremes at each side that become visible as the wearerrotates his eyes, but without re-orienting his head. The verticalcurvature 18 has a circular cross-section, and a bottom portion 20 thatextends relatively inwardly towards the face of the wearer relative toan intermediate portion 22 of the lens 12. The wrap-around configurationof the lens 12 in both the horizontal and vertical directions provides asingle view pane through which the wearer observes the externalenvironment. This configuration allows the wearer to observe objects atany location through the lens portion 12 without requiring the wearer tochange viewing environments, for example, view one object through thelens and another object at a different location outside of the viewframe of the lens. A significant advantage of this is that it reduceseye strain by allowing the wearer to view the environment through asingle wrap-around window.

It is known that light rays striking a plano lens of known constructionat a selected angle θ emerge from the lens at the angle θ but offset bya selected displacement α determinable by known formulae, as shown inFIG. 3. For example, a light ray 24 that impinges upon the lens isoffset the distance α, which is dependent upon the lens thickness, theangle of incidence and the refractive index of the lens material. Thelight ray 24 exits the lens at the angle of incidence θ. Thesevariations in the refraction of light introduce distortions into thefield of view, particularly when viewing objects along a sight line thatintersects the window obliquely. Thus, an object located at or near theperiphery of the field of view may appear elongated and/or shifted inspace relative to the actual spatial location of the object. Thisphenomena represents a common problem with conventional impact resistantface shields. Since the shields must be sufficiently thick to attainstrength, they necessarily introduce distortion effects.

Referring again to FIGS. 1 and 2, each curvature 16 and 18 of the lensportion 12 defines an arc of a circle having a substantially uniformradius. This dual-curvature configuration provides a viewing window thatis oriented almost normal to the line of sight as the wearer's eyesrotate to view objects. It produces only nominal levels of distortion,reducing the prism effects, e.g., non-uniform distortions of the field,created by the lens portion 12, and provides an optically correctedviewing window. Although a variety of radii might accrue the advantagesof the present invention, the radius of the horizontal curvature 16 ispreferably in the range between about 3 inches and about 5 inches, andmost preferably is about 4 inches. The radius of the vertical curvatureis preferably in the range between about 6.5 inches and about 8.5inches, and most preferably is about 7.4 inches. The foregoing radiusdimensions represent the distance from arbitrary center of curvaturepoints to the arc defined by each curvature of the illustrated faceshield 10. This construction defines a uniform distance to allow a fulland unobstructed viewing hemisphere.

Those of ordinary skill will readily recognize that the lens portion 12of the face shield 10 of the present invention has a thickness definedbetween outer and inner surfaces, and thus could be defined as havingmerely a single radius only when it has constant thickness. However,preferably, as shown in FIG. 4, which is a cross-sectional view of theface shield 10 of FIG. 2 taken along line 4--4, the lens portion 12 hasa thickness or depth dimension d.sub.θ along its entire arc length,which is defined between an outer facing (convex) surface 26 having aradius R1 and an inner facing (concave) surface 28 having a radius R2.In this embodiment, the radius R2 is less than the radius R1 andeccentric relative thereto. Specifically, the surfaces 26 and 28 havedifferent radii of curvatures about centers that are shifted relative toeach other. This eccentricity shifts one surface with respect to theother, to create a curved lens that has a thickness d.sub.θ that variesmonotonically away from a centerpoint, e.g., is tapered toward the edge,along the arc length of the face shield. Preferably, the inner concavesurface 28 is not completely circular, but rather one surface at leastis non-diametral to produce a minimum thickness d_(min) at the edges 30of the face shield. Furthermore, the diametral lines of the two surfacesare shifted such that the rear surface is moved back from a concentricposition, thickening the central portion of the lens to produce amaximum thickness d_(max) at or near centerline 32. As illustrated, thedistance between the centerpoint C1 for radius R1 and the centerpoint C2for radius R2 is preferably between 1 and 2 mm, but those of ordinaryskill will recognize that this distance can vary depending upon thedesired thickness of the shield at the center or at the edges of thelens in order to achieve a particular degree of bending, breaking,tensile or impact strength. According to one practice the absolute valueof the difference in centerpoints is less than the lens thicknessd.sub.θ.

As set forth above, plano (or constant-thickness) lenses introducedistortions or prismatic deviations into the field of view of the wearerby non-uniformly shifting light entering and exiting the lens. Lenseshaving truly concentric inner and outer radii, e.g., a plano lens bentinto a circular shape, introduce prismatic deviations. This prism effectdistorts, e.g., elongates or displaces, objects viewed by the wearer andthis distortion is particularly exaggerated at the peripheral viewingregions of the lens. With reference to the present invention, thevariable thickness d.sub.θ, and particularly the thinning effect of thelens at the edge regions 30, optically corrects the lens at theperipheral regions by reducing the occurrence of prismatic deviationsand overall prism imbalance. Specifically, the lensing effect of thelens 12 in conjunction with the relatively thinner edge regions 30introduce relatively low levels of distortion and serve to opticallycorrect the view over substantially the entire lens area. Thus, the term"optically-correct" as used herein is intended to refer to the reductionin prismatic deviations created by the particular design and geometry ofeach embodiment of the face shield of the invention as described abovein relation to FIGS. 1 and 2 and below in relation to FIGS. 5-7, andfurther is intended to include a face shield that exhibits a relativelylow dioptric power and a relatively low prism power over a substantialportion of the wearer's field of view. Preferably, the shield includesonly a few hundredths of a diopter of controlled dioptric power, and hasa negative lensing effect which compensates for the prism aberrations.Furthermore, by shifting the front and rear curved surfaces, astructural thickening is achieved in a central region of low distortion,allowing a lower prism thickness to be safely employed peripherally.

According to the face shield embodiment of FIGS. 1 and 2, the thicknessd_(max) of the lens 12 at the centerline 32 is about 4 mm (0.157 inches)with a minimum thickness d_(min) at the edges 30 ranging between about 2mm (0.0787 inches) and about 2.7 mm (0.102 inches). According to onepractice, the lens thickness d.sub.θ varies smoothly with increasingangle from d_(max) to d_(min). The radius R1 preferably ranges betweenabout 95 mm and about 110 mm, and most preferably between about 100 mmand about 105 mm, and the radius R2 ranges between about 96 mm and about103 mm, and most preferably is about 100 mm. For the vertical curvature18 of the lens, R1 preferably ranges between about 180 mm and 192 mm,and most preferably is about 187 mm, and R2 ranges between about 178 mmand about 186 mm, and most preferably is about 183 mm.

Furthermore, the illustrated face shield 10 has a height H1 that variesabout the length of the shield in the horizontal direction. The verticalheight H1 preferably varies between about 3.75 inches and about 4.75inches along the curvature of the shield, and preferably is about 4.25inches as measured at the centerline.

Referring again to FIGS. 1 and 2, the illustrated frame structure 14includes ventilation apertures 40 formed in a peripheral band of the topportion 34 of the face shield 10. The ventilation apertures allow air toflow through the mask, either in an upward or downward direction, toprovide for proper ventilation of the shield to resist or removefogging. The size and number of the ventilation apertures is notimportant to the teachings of the present invention. A thickness web mayprovide added strength about the ventilation openings.

According to one practice, the face shield can be mounted to the head ofthe wearer or to various sport helmets by known retention mechanisms.For example, the face shield or protector 10 can be attached to a hockeyhelmet by way of conventional securing and mounting pins, hooks, straps,and like retention elements. One end of a securing strap preferablyseats in the strap aperture 42 formed on either side of the frame member14 to help secure the face shield to the helmet and about the face ofthe wearer.

When mounted on the helmet, the face shield 10 surrounds a substantialportion of the wearer's face, and particularly surrounds the upperportion of the face as well as the nose and portions of the cheeks. Moreparticularly, the shield surrounds the face such that the inside surfaceof the lens is substantially non-oblique relative to the wearer's faceand the wearer's field of view is substantially normal to the insidesurface of the lens portion 12 of the shield 10 about most of the fieldof view. Additionally, the face shield 10 extends in the verticaldirection a distance sufficient to include a substantial portion of thedownward field of view without imposing upon the wearer the distortionsand aberrations created by the edges of the shield. Specifically, thebottom portion of the face shield extends inwardly towards the wearer'sface to allow the wearer to view the external environment through thelens portion at close distances, and through a contour which reducesobliqueness of incident rays.

The face shield 10 is composed of a transparent impact resistantmaterial, such as polycarbonate, which has a refractive index of 1.586at the helium d line. The face shield preferably meets selected strengthand impact tests, including the Canadian impact testing standard CSA §5.3.4. Those of ordinary skill will readily recognize that othersuitable polymer materials can be used.

FIGS. 5 and 6 illustrate a second embodiment of the face shield of thepresent invention. The illustrated face shield 100 has a unitary lensportion 102 that has a top portion 104 and a bottom portion 106. Thelens portion 102 also includes a horizontal curvature and a verticalcurvature that exhibit the same properties as those described above inrelation to the face shield 10 of FIGS. 1 and 2. The horizontalcurvature of the face shield approximates a semi-circle and thusprovides a wrap-around face shield that covers and protects the face ofthe wearer while providing a window portion that extends about asubstantial portion of the wearer's field of view. This wrap-aroundconfiguration of the lens 102 in both the horizontal and verticaldirections provides a single view pane through which the wearer observesthe external environment. This configuration allows the wearer toobserve objects at any location through the lens portion 102 withoutrequiring the wearer to change viewing environments, for example, viewone object through the lens and another object at a different locationoutside of the view frame of the lens.

According to one practice, the radius of the horizontal curvature ispreferably between about 3.25 inches and about 5.25 inches, and theradius of the vertical curvature is preferably in the range betweenabout 6.35 inches and about 8.35 inches, and most preferably is about7.4 inches. The foregoing radius dimensions represent the distance froman arbitrary center point to the arc defined by each curvature of theillustrated face shield 100.

The illustrated face shield 100 also has a thickness d.sub.θ that isdefined by outer and inner curved surfaces, as described above inrelation to FIGS. 1-2 and 4. the illustrated face shield 100 preferablyhas an outer radius R1 that ranges between about 95 mm and about 110 mm,and most preferably is about 103 mm, and the radius R2 ranges betweenabout 96 mm and about 103 mm, and most preferably is about 101 mm. Forthe vertical curvature of the lens 102, R1 preferably ranges betweenabout 180 mm and 192 mm, and most preferably is about 187 mm, and R2ranges between about 178 mm and about 186 mm, and most preferably isabout 183 mm.

The illustrated face shield 100 further has a height H1 that variesabout the length of the shield in the horizontal direction. The heightH1 preferably varies between about 2.3 inches and about 4.3 inches, andpreferably is about 3.3 inches at the center.

The optical and physical design properties described above in relationto shield 10 accrue to this embodiment to form an optically correct faceshield that withstands the impact of foreign bodies, without cracking orbreaking.

Referring again to FIGS. 5 and 6, the bottom portion 106 has formedthereon a molded beaded portion 110 that reinforces the bottom edge ofthe shield while eliminating sharp contours. The bottom portion 106further includes a pair of downwardly projecting tabs 112 that include amounting aperture 114 that extends therethrough. The top portion of theface shield 100 includes a set of upwardly projecting mountingprotrusions 116.

The face shield can be mounted to various sport helmets by knownretention mechanisms. For example, the face shield or protector 100 canbe attached to a football helmet 120 by way of conventional securing andmounting straps and like retention elements, as shown in FIG. 8. Theshield 100 is secured to the face guard 122 of the helmet 120 by a setof T-bolts and nuts, and the top portion 104 of the shield 100 is wedgedinto the top of the face guard frame mounted directly to the helmet 120.

When mounted on the helmet, the face shield 100 surrounds a substantialportion of the wearer's face, and particularly surrounds the nose andportions of the cheeks. More particularly, the shield surrounds the facesuch that the inside surface is substantially non-oblique relative tothe wearer's face and the wearer's field of view is substantially normalto the inside surface of the lens portion 12 of the shield 10. The faceshield also extends about the face in the horizontal direction adistance sufficient to include at least a substantial portion of thefield of view of the wearer.

FIG. 7 illustrates a third embodiment of the face shield 200 of thepresent invention. The illustrated face shield 200 has a unitary lensportion 202 that has a top portion 204 and a bottom portion 206. Thelens portion 202 also includes a horizontal curvature and a verticalcurvature that exhibit the same properties as those described above inrelation to the face shield 10 of FIGS. 1 and 2. The horizontalcurvature of the face shield approximates a semi-circle and thusprovides a wrap-around face shield that covers and protects the face ofthe wearer while providing a window portion that extends about asubstantial portion of the wearer's field of view. This wrap-aroundconfiguration of the lens 202 in both the horizontal and verticaldirections provides a single view pane through which the wearer observesthe external environment. This configuration allows the wearer toobserve objects at any location through the lens portion 202 withoutrequiring the wearer to change viewing environments, for example, viewone object through the lens and another object at a different locationoutside of the view frame of the lens.

According to one practice, the radius of the horizontal curvature of theface shield 202 is preferably between about 3 inches and about 5.5inches, and most preferably is about 4 inches, and the radius of thevertical curvature is preferably in the range between about 6.5 inchesand about 8.5 inches, and most preferably is about 7.4 inches. Theforegoing radius dimensions represent the distance from an arbitrarycenter point to the arc defined by each curvature of the illustratedface shield 200.

The illustrated face shield 100 also has a thickness d.sub.θ that isdefined by outer and inner curved surfaces, as described above inrelation to FIGS. 1-2 and 4. The illustrated face shield 200 preferablyhas an outer radius R1 that ranges between about 95 mm and about 110 mm,and most preferably is about 104 mm, and the radius R2 ranges betweenabout 96 mm and about 105 mm, and most preferably is about 101 mm. Forthe vertical curvature of the lens 202, R1 preferably ranges betweenabout 180 mm and 192 mm, and most preferably is about 188 mm, and R2ranges between about 178 mm and about 186 mm, and most preferably isabout 184 mm.

The lens portion further has a pair of downwardly projecting portions210 that extend below an intermediate portion 212 to form secondary lensportions. These portions preferably have a radius between about 1.0 inchand 2.0 inches. The illustrated face shield 200 has a height H1 definedat the intermediate portion 212 that ranges between 3.5 inches and about4.1 inches. The height H2 of the lens portion other than at theintermediate portion varies about the length of the shield in thehorizontal direction. The height H2 preferably varies between about 4inches and about 5 inches, and preferably is about 4.25 inches.

The optical and physical design properties described above in relationto shield 10 accrue to this embodiment to form an optically correct faceshield that withstands the impact of foreign bodies, without cracking orbreaking.

Referring again to FIG. 7, the bottom portion 206 has formed thereon amolded beaded portion 220 that reinforces the bottom edge of the shieldwhile eliminating sharp contours. The beaded portion extendssubstantially about the entire periphery of the shield 200. The shieldalso includes ventilation apertures 240 formed in the top portion 234 ofthe bead. The ventilation apertures allow air to flow through the mask,either in an upward or downward direction, to provide for properventilation of the shield to resist fogging and aid clearing of thelens. The size and number of the ventilation apertures is not importantto the teachings of the present invention.

The face shield can be mounted to various sport helmets by knownretention mechanisms. For example, the face shield 200 can be attachedto a hockey helmet 250 by way of conventional pins, hooks, and securingand mounting straps, and like retention elements, as shown in FIG. 9.

When mounted on the helmet, the face shield 200 surrounds a substantialportion of the wearer's face, and particularly surrounds the nose andportions of the cheeks. More particularly, the shield surrounds the facesuch that the inside surface is substantially non-oblique relative tothe wearer's face and the wearer's field of view is substantially normalto the inside surface of the lens portion 202 of the shield 200. Theface shield also extends about the face in the horizontal direction adistance sufficient to include substantially the entire field of view ofthe wearer. The secondary lens portions 210 further project downwardlyto ensure capture of a substantial portion of the downward field ofview.

The face shields of the invention shown and described above can be madefrom known processes and techniques, such as injection molding.

The impact resistant face shield constructed according to the featuresof the present invention can be employed in a wide range of environmentsand for a wide range of uses. For example, the face shield shown anddescribed above in relation to FIGS. 1-7 can be used by individuals forrecreational and sporting activities in addition to football and hockey,such as skiing, roller-blading, soccer, basketball, baseball, lacrosseand other like activities. The face shield can also be employed in otherindustries by amateurs and/or professionals, such as by carpenters andmedical personnel.

It will thus be seen that the invention efficiently attains the objectsset forth above, among those made apparent from the precedingdescription. Since certain changes may be made in the aboveconstructions without departing from the scope of the invention, it isintended that all matter contained in the above description or shown inthe accompanying drawings be interpreted as illustrative and not in alimiting sense.

It is also to be understood that the following claims are to cover allgeneric and specific features of the invention described herein, and allstatements of the scope of the invention which, as a matter of language,might be said to fall therebetween.

Having described the invention, what is claimed as new and desired to besecured by Letters Patent is:
 1. An arcuately molded face shield formounting to sporting helmets suitable for use in sporting events, saidface shield comprising:a unitary, optically-correct lens portion forshielding against mechanical impact a substantial portion of a sportparticipant's face having, in a first orientation, a first curvatureextending in a horizontal direction and a second curvature extending ina vertical direction, said vertical curvature terminating in a topportion and a bottom portion, said bottom portion extending relativelyinwardly towards the face of the participant relative to an intermediateportion of said lens disposed between the top and bottom portions whenmounted to the sporting helmet, and frame means forming a frameintegrally formed with and disposed about a portion of the periphery ofsaid optically-correct lens portion in an as-molded condition, whereinsaid frame has a top portion, and further including ventilation meansformed in said top portion of said frame for allowing air to pass freelytherethrough.
 2. A face protective shield for activity, comprising:ashield body formed of strong clear polymeric material and having aperipheral region and a central region, the peripheral region includingmeans for attaching to secure the shield body in front of a wearer'sface, and the central region forming a viewing window sized to extendsubstantially entirely around in front of the wearer's face and having athickness effective to survive impact without cracking, said thicknessfurther introducing prism viewing aberrations, and said central regioncurves in horizontal and vertical planes over substantially the entirecentral region to introduce a degree of lensing and correct said viewingaberrations, wherein the central region has front and rear surfaces,wherein a radius of curvature R_(f) of said front surface is greaterthan a radius of curvature R_(r) of said rear surface, and wherein R_(f)-R_(r) =δ, and centers of curvature of said front and rear surfaces arespaced closer than δ.
 3. A face protective shield according to claim 2,wherein said central region has different front and back surfacecurvatures in a horizontal plane, and different front and back surfacecurvatures in a vertical plane, forming an arched central region havinglensing power in two dimensions and with a greater central thicknessthan edge thickness.
 4. A face protective shield according to claim 3,wherein said lensing power is negative in at least said horizontalplane.
 5. A face protective shield consisting of a single molded sheetof polycarbonate curving about substantially 180° in a horizontal planewith a front diameter effective to fit around the face of a wearer andhaving different front and back surface radii of curvature about centersthat are shifted to effectively correct vision throughout said shieldwhile enhancing strength thereof.
 6. An arcuately molded face shield formounting to sporting helmets suitable for use in sporting events, saidface shield comprising:a unitary, optically-correct lens portion forshielding against mechanical impact a substantial portion of a sportparticipant's face, having, in a first orientation, a first curvatureextending in a horizontal direction and a second curvature extending ina vertical direction, said vertical curvature terminating in a topportion and a bottom portion, said bottom portion extending relativelyinwardly towards the face of the participant relative to an intermediateportion of said lens disposed between the top and bottom portions whenmounted to the sporting helmet, wherein said optically-correct lensportion has a variable thickness that reduces distortions about theparticipant's field of view.
 7. The face shield of claim 6, wherein saidthickness of said optically-correct lens varies monotonically away froma centerpoint of said lens along said horizontal direction.
 8. A faceprotective shield for activity, comprising:a shield body formed ofstrong clear polymeric material and having a peripheral region and acentral region, the peripheral region including means for attaching tosecure the shield body in front of a wearer's face, and the centralregion forming a viewing window sized to extend substantially entirelyaround in front of the wearer's face and having a thickness effective tosurvive impact without cracking, said thickness further introducingprism viewing aberrations, and said central region curves in horizontaland vertical planes over substantially the entire central region tointroduce a degree of lensing and correct said viewing aberrations,wherein said optically-correct lens portion has a variable thicknessthat reduces distortions about the participant's field of view.
 9. Theface shield of claim 6, wherein said thickness of said optically-correctlens varies monotonically away from a centerpoint of said lens alongsaid horizontal plane.
 10. An arcuately molded face shield for mountingto sporting helmets suitable for use in sporting events, said faceshield comprisinga unitary, optically-correct viewing window defining afield of view for shielding against mechanical impact a substantialportion of a sport participant's face having, in a first orientation, afirst curvature extending in a horizontal direction and a secondcurvature extending in a vertical direction, and wherein saidoptically-correct viewing window has a variable thickness to reducedistortions in said field of view.
 11. The face shield of claim 10,wherein said thickness of said viewing window varies monotonically awayfrom a centerpoint of said window.
 12. The face shield of claim 10,wherein said optically-correct viewing window comprises ventilationmeans formed in a top portion thereof for allowing air to pass freelytherethrough.
 13. The face shield of claim 10 wherein saidoptically-correct viewing window has a first distal end portion disposedon one end of the horizontal curvature of the lens, a second distal endportion disposed on an opposed end of the horizontal curvature, and agenerally vertically extending intermediate portion disposed between thefirst and second distal portions, wherein at least portions of saidfirst and second distal portions extend downwardly beyond saidvertically-extending intermediate portion to form secondary windowportions.
 14. The face shield of claim 13, wherein said verticallyextending intermediate portion of said optically-correct viewing windowhas a first selected height h₁ measured between the top and bottomportions of the optically-correct window that is in the range betweenabout 3.5 inches and about 4.1 inches, andsaid secondary window portionshaving a height h₂ defined between the top portion of the lens and thebottom portion of the lens that is in the range between about 4.0 inchesand about 5.0 inches.
 15. The face shield of claim 10, wherein saidfirst curvature of said optically-correct viewing window has a radius inthe range between about 3.0 inches and about 5.0 inches.
 16. The faceshield of claim 10, wherein said second curvature of saidoptically-correct viewing window has a radius in the range between about6.5 inches and about 8.5 inches.
 17. The face shield of claim 10,wherein each said secondary window portion has a radius in the rangebetween about 1.0 inches and about 2.0 inches.
 18. The face shield ofclaim 10, wherein said horizontal portion of said optically-correctviewing window has a first distal portion and an opposed second distalportion and an intermediate portion disposed therebetween, and whereinsaid lens portion has a height h₁ measured between the top and bottomportions of the lens that varies between the first and second distalportions, said height h₁ being in the range between about 3.75 inchesand about 4.75 inches.
 19. The face shield of claim 10, wherein saidfirst curvature has a radius in the range between about 6.35 inches andabout 8.35 inches.
 20. The face shield of claim 19, wherein said secondcurvature has a radius in the range between about 6.35 inches and about8.35 inches.
 21. The face shield of claim 10, wherein said viewingwindow has an inner surface and an outer surface that define saidthickness of said window, said outer surface having a radius ofcurvature different from the radius of curvature of said inner surface.22. The face shield of claim 10, wherein said variable thickness of saidwindow has a maximum thickness d_(max) of about 4 mm, and a minimumthickness d_(min) in the range between about 2 mm and about 2.7 mm. 23.The face shield of claim 21, wherein said radius of curvature of saidinner surface is eccentric relative to said radius of curvature of saidouter surface and smaller than said radius of said outer surface. 24.The face shield of claim 21, wherein said radius of curvature of saidouter surface ranges between about 95 mm and about 110 mm.
 25. The faceshield of claim 21, wherein said radius of curvature of said innersurface ranges between about 96 mm and about 103 mm.